2.4GHz DSS DIGITAL CORDLESS HEADSET
MODEL : DA579
USA VERSION
BACKMI Corporation
RF Circuit Description
LO Generation :
The LO signal is generated by a programmable PLL frequency synthesizer in the
U901(RF109) and the an external 2.4GHz VCO(U903). The RF109 synthesizer requires differential
input signals from the external VCO to generate the LO Frequency.
Therefore a BALUN(U905) transformer is used to generate differential signals from single-ended VCO
output.
Receive Path :
The signal is received at the antenna and pass the T/R switch(U802) and an RF
bandpass filter. The output of the bandpass filter is ac-coupled to the Low Noise Amplifier (LNA) of
the U901.
The U901 downconverts the RF signal into In-phase( I) and Quadrature signal(Q) baseband signals.
The differential I and Q baseband signals are dc-coupled to the ASIC(U1 or U303) RXIP, RXIN, RXQP
and RXQN inputs.
Transmit Path
Base unit :
The baseband digital data input signal is shaped by external filter (R919,C925, L901,
C924, R918) and inputted to the TXD1 Port of the U901 (RF109).
The inputted baseband digital data is mixed with Carrier supplied to VCO (U903) and transmitted to
the U801 (RF110) with a phase difference of 180 degreed between the two branch.
The inputted a differential signals to the U801 (RF110) are amplified by the U801 (RF110) And the
differential output signals of the U801 (RF110) output port are converted to a single- Ended signal at
the RF matching network.
Handset :
The baseband digital data input signal is shaped by external filter (R919,C925, L901,
C924, R918) and inputted to the TXD1 Port of the U901 (RF109).
The inputted baseband digital data is mixed with Carrier supplied to VCO (U903) and transmitted to
the Q901. The inputted a single-Ended signals is amplified by the Q900, Q901
